The invention describes a method for using nanosized semiconductor materials to decompose toxic organic materials and more particularly, to a method of using MoS.sub.2 nanosized particles to decompose aromatic and halogenated hydrocarbons by photo-oxidation.
Contamination of sediments and aqueous water systems by halogenated organic compounds presents a serious environmental threat due to their toxicity and resistance to biodegradation. These chemicals are widely employed as pesticides, insecticides, and wood preservatives and thus are ubiquitous in the environment of both industrialized and agrarian nations. Even chemicals that have been banned for years, like dichlorodiphenyltrichloroethane (DDT) and its analogues, still pose major environmental threats. A subgroup of these toxic chemicals, referred to as chlorinated aromatics, includes chlorinated benzenes and biphenyls (PCBs), pentachlorophenol (PCP) and insecticides such as DDT.
In general, the more halogenated atoms, such as chlorine, on the aromatic phenol ring, the greater the biohazard. The widespread proliferation of PCP and its analogues in the environment can also result from combustion, water treatment with chlorine in the presence of organic materials, and municipal sewage treatment plants and incinerators. Once discharged into the environment, these water insoluble compounds seep into the sediment of rivers, lakes, and other bodies of water and continually leach out into the water supply, potentially affecting the entire mammalian food chain.
Microbial degradation and naturally occurring hydrolysis of these compounds is a very slow process (for example, for 4-cholorophenol at 9.degree. C., the half life is nearly 500 days). Some direct photo-degradation also occurs, though the limited absorbance of chlorinated aromatics above 350 nm makes this process painfully slow. Sometimes this direct photolysis can actually lead to more toxic products. Direct photolysis of PCP has been reported to lead to octachlorodibenzo-p-dioxin, an even more toxic species than its precursor.
Effective methods of treatment of these chlorinated aromatics are being sought. Photocatalytic oxidation of these compounds to form harmless CO.sub.2 and HCI, a process referred to as total mineralization has been investigated. The semiconductor catalyst of choice in these studies has generally been TiO.sub.2, a white, photostable, non-toxic powder, whose principal deficiency is an absorbance edge which starts at about 385 nm, allowing less than 3% utilization of the solar spectrum. Serpone (Serpone, N., Res. Chem. Intermed., 1994, 20, 9, 953-992) provides a description of the use of TiO.sub.2 in heterogeneous photocatalysis to detoxify various organic materials. Serpone observes that TiO.sub.2 absorbs only about 3% of solar radiation and thus is not very efficient in using natural light to decompose toxic organic compounds.
It would be useful to have a visible-light-absorbing semiconductor catalytic material available that is photostable and non-toxic and that can utilize visible light to decompose toxic organic materials. Thurston and Wilcoxon (Thurston, T. and Wilcoxon, J., The J. of Physical Chemistry, 1999, 103, 1, 11-17; incorporated by reference herein) demonstrate the use of new MOS.sub.2 photocatalysts to destroy phenol, and demonstrated a strong effect of size or band-gap on the rate of photo-oxidation.